1. Field of the Invention
The invention relates to a machine tool apparatus (machining center) for machining a workpiece, and more particularly to a machining apparatus provided with a machine tool holder that is replaceably mounted on or in a spindle.
2. Description of the Related Art
Conventionally, a machine tool apparatus performs various types of machining operations on workpieces, for example, components of an automatic transmission (hereinafter referred to as “A/T”). These machining operations include at least one process performed in a direction that is oblique to the axis of the spindle of the machine tool apparatus.
For the type of machine tool that machines obliquely with respect to the spindle, Japanese Patent Laid-Open No. 2001-138176 proposes a numerical control apparatus (hereinafter referred to as “NC”) for machining an oblique hole in a workpiece. The NC machine tool apparatus disclosed in this publication machines a hole in the workpiece that is oblique to the spindle by using a three directional feed mechanism to execute feed control of the machine tool in the X axis, Y axis and Z axis (spindle) directions.
However, with the NC machine tool apparatus disclosed in the above-mentioned publication, while machining the oblique hole in the workpiece it is necessary to execute three-directional feed control of the machining tool in the X axis, Y axis and Z axis (spindle) directions. Accordingly, the machining control is complicated and cumbersome, and a large number of different programs for feed control of the machining tool are necessary. As a result, the expenditure on programs is substantial. Moreover, the feed mechanism is also complicated since it is necessary to execute movement in three axial directions, namely, the two axial directions (the X and Y axes) in which a table is moved, and the spindle (the Z axis) direction.